1. Field of the Invention
The invention relates to the field of clocking signals for use with digital circuits, particularly graphics processors and the like.
2. Prior Art
Most typically, in digital computers an oscillator is used to provide timing signals or a plurality of synchronized timing signals which control the operation of components or elements in the computer. In some cases, certain components of the computer are able to operate at higher speeds than others, and an operational advantage can be obtained by operating the faster components at the faster rate. Controlling the operation of components that operate at different rates is a problem which must be overcome to obtain this advantage.
U.S. Pat. No. 4,677,433 discloses the operation of a microprocessor (8086) at one speed and a coprocessor at another speed. For the embodiment described in this patent, an 8086 microprocessor operates at a frequency of 10 MHz; the coprocessor (a numeric data processor, Intel Pat No. 8087-3) at a frequency of 5 MHz. The patent describes operating the 8086 at a lower frequency when the microprocessor is operating with the coprocessor, and operating the microprocessor at its higher rate at other times. In the case of this disclosure, both the higher and lower clock frequencies are synchronized. This makes the task of switching between clocking signals relatively simple.
Applicant believes there are many computers where different components operate at different frequencies; but generally, and particularly where the components need to directly interact, synchronized clocking/timing signals are used.
As will be seen with the present invention, a graphics processor and a frame buffer are operated at two different asynchronous clock rates. This presents special problems in switching from one clocking signal to the other.